function animate(obj,target,callback){
    clearInterval(obj.timer);
      obj.timer = setInterval(function(){
      var step = Math.ceil(target - obj.offsetLeft) / 10;
      step = step > 0 ?Math.ceil(step) : Math.floor(step);
      if(obj.offsetLeft == target){
              clearInterval(obj.timer);
               callback && callback();
          }
          obj.style.left = obj.offsetLeft + step + 'px';
      },15);
  }